Recent rapid advances in 3D computer graphics technologies have enabled synthesis of images comparable in quality to photographed images. However, synthesis of high-quality images still requires both excessive calculation times of computers and working hours of designers. Much research and development efforts have been made to solve this problem.
The sense of realism in computer generated imagery (CGI) is affected by various factors, in particular, surface materials of scene elements. Rendering materials having complex physical surface phenomena, such as skins or hairs of a body, fine cloths and mixed paints, requires many considerations. In case of objects composed of these materials, the color and brightness of them may look differently depending upon viewing directions and lighting directions. In some cases, material properties are obtained as raw data by photographing surfaces of real objects, or modeled using algebraic equations, and then reproduced through computer graphics.